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r"""Implementation of the d_{\Delta^*} metric.

Defined as: d_{\Delta^*}(s, t) = \max_{a\in A} |Q*(s, a) - Q*(t, a)|
"""

import numpy as np
from rl_metrics_aaai2021 import metric


class DDeltaStar(metric.Metric):
  r"""Implementation of the d_{\Delta^*} metric."""

  def _compute(self, tolerance, verbose=False):
    del tolerance
    assert self.env.q_values is not None, 'Q-Values have not been computed.'
    self.metric = np.max(np.abs(self.env.q_values[:, None, :] -
                                self.env.q_values[None, :, :]), axis=-1)
    self.statistics = metric.Statistics(0., 0., 0, 0.)
